Tom de Vries <tom_devr...@mentor.com> writes: >> Why not just collect the usage information at >> the end of final rather than at the beginning, so that all splits during >> final have been done? > > If we have a call to a leaf function, the final rtl representation does not > contain calls. The problem does not lie in the final pass where the callee is > analyzed, but in the caller, where information is used, and where the unsplit > call is missing the clobber of r6.
Ah, so when you're using this hook in final, you're actually adding in the set of registers that will be clobbered by a future caller's CALL_INSN, as well as the registers that are clobbered by the callee itself? That seems a bit error-prone, since we don't know at this stage what the future caller will look like. (Things like the target attribute make this harder to predict.) I think it would be cleaner to just calculate the callee-clobbered registers during final and leave the caller to say what it clobbers. FWIW, I still think it'd be better to collect the set at the end of final (after any final splits) rather than at the beginning. >> For other cases (where the usage isn't explicit >> at the rtl level), why not record the usage in CALL_INSN_FUNCTION_USAGE >> instead? >> > > Right, we could add the r6 clobber that way. But to keep things simple, I've > used the hook instead. Why's it simpler though? That's the kind of thing CALL_INSN_FUNCTION_USAGE is there for. Thanks, Richard
